Developing method for electrophotography

ABSTRACT

A developing method for electrophotography comprises the provision of a corona-ion shield member between a developing electrode for developing an electrostatic latent image and a charger disposed adjacent to the developing electrode, to thereby prevent the developing electrode from being charged with corona ions from the charger.

United States Patent Soma et al. 1 Jan. 1, 1974 DEVELOPING METHOD FOR 3,543,023 11/1970 Yellin et al. 317/262 A ELECTROPHOTOGRAPHY 3,620,617 1 1/1971 Kelly et al. 250/496 ZC Inventors: Ikuo Soma, Tokyo; Yujiro Ando,

Yokohama, both of Japan Canon Kabushiki Kaisha, Tokyo, Japan Filed: July 31, 1972 Appl. No.: 276,368

Assignee:

U.S. Cl. 1. 317/262 A, 96/1 R Int. Cl. H0lt 19/00 Field of Search 317/262 A;

250/495 ZC; 96/1 R, 1 A, 1 C

References Cited UNITED STATES PATENTS 7/1954 Mayo et al 317/262 A Primary Examiner-William M. Shoop, Jr. Assistant Examiner-Harry E. Moose, Jr. Att0rney-.loseph M. Fitzpatrick et al.

8 Claims, 4 Drawing Figures PATENTEU 1 74 FIG. 4

FIG. 2

DEVELOPING METHOD FOR ELECTROPHOTOGRAPHY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to'a method which uses a de-- veloping electrode to develop an electrostatic latent image formed by an electrophotography, electrostatic recording or other process, and more particularly to a method of insulating the developing electrode from other charging electrodes to thereby prevent such electrode from being excessively charged by those other electrodes.

2. Description of the Prior Art It is known to use a developing electrode to develop an electrostatic latent image formed by an electrophotography, electrostatic recording or other process. In this case, various attempts to enhance the developing effect have been made such as selection of the relative condition between the developing electrode and the photosensitive medium, and adjustment of the voltage applied to the developing electrode.

When a developing electrode is used to develop a latent image, however, the developing effect may vary with such factors as the state of the electrostatic latent image on the photosensitive medium, the distance between the photo-sensitive medium and the developing electrode, the voltage applied to the developing electrode, etc., and it is difficult to correlate such factors and accordingly to ensure that an excellent development is achieved.

That is even if a predetermined voltage is applied to the developing electrode, the state of the electrostatic latent image is variable with extraneous factors such as ambient temperature and humidity, thus making it difficult to obtain a uniform developing effect.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS Other objects of the present invention will become fully apparent from the following detailed description taken in conjunction with theaccompanying drawings,

in which:

FIG. 1 illustrates an example of the electrophotographic process to which the present invention is applicable; 1

FIG. 2 is a view illustrating the effect of the developingelectrode insulated from others; and

FIGS. 3 and 4 illustrate embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown an example of an electrophotographic process for forming and develop ing an electrostatic latent image. A drum 1 comprises a three-layer photosensitive medium consisting of a dielectric layer 2, a photoconductive layer 3 and a conductive substrate 4. Around the drum 1 there are disposed a primary charger 5, a corona charger 6 for use during the effecting of an exposure on drum 1, a developing electrode 7 and a charger 8 for transferring a developed image to a transfer medium. When it is desired to form on the photosensitive medium 1 an electrostatic latent image having dark areas of positive polarity by using an N-type-semi-conductor such as CdS with the above-described arrangement and to develop such an image by means of toner of negative polarity, fogging of the developed image by applying a bias to the developing electrode 7 so as to provide a potential which is positive with respect to the surface potential on the light areas of the image. The dark areas of the image may be developed in accordance with the differ ence between the potential of the electrostatic latent image on the photosensitive medium and the potential of the developing electrode. Since the potential of the developing electrode is predetermined, the density of the image will be varied if the potential of the latent image on the photosensitive medium is varied with variations in environmental factors (especially temperature and humidity). This would raise difficulties in setting the potential of the electrostatic latent image. However, by insulating the developing electrode from the others, a charge will be induced on the developing electrode in accordance with the potential of the latent image on the photosensitive medium and thus, the charge on the entire developing electrode will be balanced with respect to the positive and negative polarities. As a result, the potential of the developing electrode may always be maintained between the potential of the light areas of the latent image and the potential of the dark areas of the latent image. This means that fogless development may be achieved regardless of any variation in the latent image on the photosensitive medium which would result from the variable environmental factors. Also, the insulation of the developing electrode from the others will lead to the creation of an effect referred to as self-bias effect, which is effective to increase the contrast of the electrostatic latent image and thus provide a higher definition of the developed image.

FIG. 2 illustrates such self-bias effect. In this figure, numeral 11 designates the conductive substrate, 12 the photoconductive layer, 13 the dielectric layer, and 14 the developing electrode. It should be understood that the conductive substrate 11 is grounded and the developing electrode is insulated from others. If an electrostatic latent image a of positive polarity, for example, exists on the surface of the dielectric layer, a charge b of negative polarity will be induced on the corresponding portion of the developing electrode 14. However, since the developing electrode 14 is a conductive material insulated from others as described previously, a charge 0 of different polarity from the induced charge b will be produced on the other portion of the developing electrode than that portion in which the induced charge b exists, thus nullifying the charge on the entire developing electrode. The charge c will in turn induce a charge d in the portion of the photosensitive layer which corresponds to the portion of the electrode carrying the charge 0. As the result of such effects, in the portion of the photosensitive medium which has no latent image of positive polarity, the developing toner (which may be of negative polarity if a positive image is to be provided) will be attracted from the photosensitive layer toward the developing electrode to thereby prevent said portion of the photosensitive medium from being developed, thus providing a fogless, excellent image.

However, if the insulation of the developing electrode from others should then be destroyed, the aforesaid self-bias effect would be reduced to cause the image to lose its definition.

The process shown in FIG. 1 will now be described more specifically. When the corona ions of negative polarity leaving the charger6 impinge on the developing electrode 7, they will neutralize the positive charge in FIG. 2, thus preventing the charge d from being induced. Thus, the charge on the entire developing electrode will not be nullified, and instead will tend to create fogging. In view of this, the present invention prevents corona ions from being applied to the developing electrode insulated from others, thereby ensuring a fogless, clear image to be obtained. Various methods of blocking the flow of corona ions may come to mind, but a simple and inexpensive method will be described hereunder. An insulating member may be disposed in the path of the corona ions flowing to the developing electrode so that the insulating member may be charged with the corona ions to repulse any further corona ions thereafter and thus prevent them from reaching the developing electrode.

FIG. 3 illustrates a specific arrangement for achieving such a result. As shown there, a corona-ion shield member 31 formed of insulative material is interposed between the charger 6 and the developing electrode 7. Any corona ion moving from the charger 6 toward the developing electrode 7 may thus be blocked by the shield member 31 and cannot reach the electrode 7. The shielding effect for the corona ions depends on the distance from the shield member 31 to the outermost surface of the photosensitive medium 1, and a distance of mm or less has empirically been found practical. Most preferably, the distance may be 2 mm or less.

Alternatively, the shield member 31 may be disposed between the transfer charger 8 and the developing electrode 7 to block the corona ions from the charger 8. Another shield means of insulative material may be provided adjacent to the charger 8, as indicated at 32. In this latter case, the insulative member 32 located adjacent to the transfer charger 8 may be well charged to repulse the corona ions and thus, it is highly effective to prevent the tendency of corona ions to flow toward the developing electrode 7.

The locations of the shield members 31 and 32 may be reversed. If these shield members are formed of a conductive material, they may be grounded to attract corona ions or alternatively may be ungrounded so as to be charged in a manner similar to the insulative material, thereby repulsingsubsequent corona ions with a result that a good corona-ion shielding effect is achieved. Thus, the shield members may be formed not only of an insulative material but also of a conductive material.

If space for the corona-ion shield member is not available in the shown locations, air may be blown over the photosensitive medium 1 in the direction from the developing electrode toward the charger 6 or 8, with the same result as that obtained by the provision of the corona-ion shield members. Actually, the air flow is directed as shown by the arrows 41 indicated in FIG. 4.

The data in the experiments carried out by the inventors will be shown below. When the potential of the electrostatic latent image on the photosensitive medium was set to 0 volt for the light areas and to H400 volts for the dark areas, the potential of the developing electrode proved to be lowerthan r+30 volts in the case of ordinary original images (such as newspapers, journals, etc.), whereas the potential of the developing electrode was raised to the level of +50 to volts by using the method as shown in FIGS. 3 or 4. Especially, the use of the shield members 31 and 32 as shown in FIG. 3 proved to be the most efficient.

We claim:

1. In an electrophotographic process utilizing a developing electrode disposed in face-to-face relation with an electrostatic latent image formed on a carrier device, a method of preventing undesirable charging of the developing electrode comprising the steps of insulating said developing electrode to permit a self-bias to be induced thereon during developing of a said electrostatic latent image, and shielding said developing electrode from said corona discharge electrodes to prevent ions produced by said corona discharge electrodes from affecting the self-bias produced on said developing electrode.

2. In a developing device for use in an electrophotographic apparatus including a device for carrying an electrostatic latent image, and at least one corona discharge device for use in producing a photocopy on said apparatus, the improvement comprising: an insulated developing electrode, and means mounting said developing electrode in a face-to-face relationship with a said electrostatic image carried on said carrier device wherein a self-bias is effected on said developing electrode due to its close proximity to a said electrostatic latent image; means for supplying a developer between said carrier and said developing electrode; and coronaion shielding means disposed between said corona discharge device and said developing electrode for preventing corona-ions generated by said corona discharge device from being deposited on said developing electrode.

3. A developing device for use in electrophotography, according to claim 2, wherein said corona-ion shielding means extends outwardly from said carrier device and is disposed within 5 mm of the surface of said carrier device which bears said electrostatic latent image.

4. A developing device according to claim 2, wherein said corona-ion shielding means is formed of an insulative material.

5. A developing device according to claim 2, wherein said corona-ion shielding means is formed of an insulated conductive materialf 6. A developing device according to claim 2, wherein said corona-ion shielding means is formed of v a grounded conductive material.

7. A developing device according to claim 2, wherein said corona-ion shielding means is disposed adjacent to said corona discharge device.

8. In a developing device for use in an electrophotographic apparatus including a device for carrying an electrostatic latent image, and at least one corona discharge device for use in producing a photocopy on said apparatus, the improvement comprising: an insulated developing electrode, and means mounting said developing electrode in a faceto-face relationship with a said electrostatic image carried on said carrier device wherein a self-bias is effected on said developing electrode due to its close proximity to a said electrostatic latent image; means for supplying a developer between said carrier and said developing electrode; and means for blowing air into the space between said developing bias effect is unaffected by said ions.

' UNITED STATES PATENT OFFICE CERTIFICATE CORRECTION Patent; No. 3,783352 Dated Januery l, 1974 Inventofl) IKICJO SOMA,',ET AL'. I

It is certified that error appears in the above-identified patent and that said LettersPatent are hereby corrected as shownbe'low: 1-

Column 1, line 32, after "That is" insert Column 2, line 15, after "image" insert --may be aVoided-;

Column 3, linef.64, "member" should read "members- Signedand sealed this 18th day of" June (SEAYL) Attest:

EDWARD M .FI.|ETCHER,'JR. w H c. MARSHALL 1mm v Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION".

Patent No. ,783352 Dated January 1, 1974 Inventor) IKI JO SOMA, ET AL. T It is certified that error appears in the above-identified patent and that; said Letters Patentare hereby corrected a s shownbelow: Column 1, line 32, after "That is" insert Column 2, line .15, after "image" insert ma y be avoided-w T Column 3, line 64, "member" should read '-member:s--.

Signed 5nd; sealed this 18th day of" June 197lL.'-

(SEAL) 1 T Attestp EDWARD M.FLE1CHER,'JR. M t r c. MARSHALL mum V A ttetsting Officer Commissioner of Patents FORM po'mso oscc uy-oc scanen i 

1. In an electrophotographic process utilizing a developing electrode disposed in face-to-face relation with an electrostatic latent image formed on a carrier device, a method of preventing undesirable charging of the developing electrode comprising the steps of insulating said devEloping electrode to permit a selfbias to be induced thereon during developing of a said electrostatic latent image, and shielding said developing electrode from said corona discharge electrodes to prevent ions produced by said corona discharge electrodes from affecting the self-bias produced on said developing electrode.
 2. In a developing device for use in an electrophotographic apparatus including a device for carrying an electrostatic latent image, and at least one corona discharge device for use in producing a photocopy on said apparatus, the improvement comprising: an insulated developing electrode, and means mounting said developing electrode in a face-to-face relationship with a said electrostatic image carried on said carrier device wherein a self-bias is effected on said developing electrode due to its close proximity to a said electrostatic latent image; means for supplying a developer between said carrier and said developing electrode; and corona-ion shielding means disposed between said corona discharge device and said developing electrode for preventing corona-ions generated by said corona discharge device from being deposited on said developing electrode.
 3. A developing device for use in electrophotography, according to claim 2, wherein said corona-ion shielding means extends outwardly from said carrier device and is disposed within 5 mm of the surface of said carrier device which bears said electrostatic latent image.
 4. A developing device according to claim 2, wherein said corona-ion shielding means is formed of an insulative material.
 5. A developing device according to claim 2, wherein said corona-ion shielding means is formed of an insulated conductive material.
 6. A developing device according to claim 2, wherein said corona-ion shielding means is formed of a grounded conductive material.
 7. A developing device according to claim 2, wherein said corona-ion shielding means is disposed adjacent to said corona discharge device.
 8. In a developing device for use in an electrophotographic apparatus including a device for carrying an electrostatic latent image, and at least one corona discharge device for use in producing a photocopy on said apparatus, the improvement comprising: an insulated developing electrode, and means mounting said developing electrode in a face-to-face relationship with a said electrostatic image carried on said carrier device wherein a self-bias is effected on said developing electrode due to its close proximity to a said electrostatic latent image; means for supplying a developer between said carrier and said developing electrode; and means for blowing air into the space between said developing electrode and said corona discharge device in the direction away from said developing electrode and toward said corona discharge device, wherein the flow of said air is maintained to prevent corona-ions generated by said corona discharge device from being deposited on said developing electrode, whereby said self-bias effect is unaffected by said ions. 